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goldsteinngoldsteinn
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[ValueTracking] Use select condition to help infer bits of arms
If we have something like `(select (icmp ult x, 8), x, y)`, we can use the `(icmp ult x, 8)` to help compute the knownbits of `x`.
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-10
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3 files changed

+24
-10
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‎llvm/lib/Analysis/ValueTracking.cpp

Lines changed: 14 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1026,6 +1026,20 @@ static void computeKnownBitsFromOperator(const Operator *I,
10261026
computeKnownBits(I->getOperand(2), Known, Depth + 1, Q);
10271027
computeKnownBits(I->getOperand(1), Known2, Depth + 1, Q);
10281028

1029+
// See what condition implies about the bits of the two select arms.
1030+
if (!Known.isConstant()) {
1031+
KnownBits KnownFromCond(Known.getBitWidth());
1032+
computeKnownBitsFromCond(I->getOperand(2), I->getOperand(0),
1033+
KnownFromCond, Depth + 1, Q, /*Invert=*/true);
1034+
Known = Known.unionWith(KnownFromCond);
1035+
}
1036+
if (!Known2.isConstant()) {
1037+
KnownBits KnownFromCond(Known2.getBitWidth());
1038+
computeKnownBitsFromCond(I->getOperand(1), I->getOperand(0),
1039+
KnownFromCond, Depth + 1, Q, /*Invert=*/false);
1040+
Known2 = Known2.unionWith(KnownFromCond);
1041+
}
1042+
10291043
// Only known if known in both the LHS and RHS.
10301044
Known = Known.intersectWith(Known2);
10311045
break;

‎llvm/test/Analysis/ScalarEvolution/max-expr-cache.ll

Lines changed: 6 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -226,21 +226,21 @@ define void @umax(i32 %tmp3) {
226226
; CHECK-NEXT: %tmp48 = select i1 %tmp47, i32 %tmp44, i32 %tmp46
227227
; CHECK-NEXT: --> ((7 + (256 umin {%tmp3,+,-256}<%bb4>))<nuw><nsw> umax (256 umin (1 + (256 umin (1 + (256 umin (1 + (256 umin (1 + (256 umin (1 + (256 umin (1 + (256 umin (1 + (256 umin {%tmp3,+,-256}<%bb4>))<nuw><nsw> umin {%tmp3,+,-256}<%bb4>))<nuw><nsw> umin {%tmp3,+,-256}<%bb4>))<nuw><nsw> umin {%tmp3,+,-256}<%bb4>))<nuw><nsw> umin {%tmp3,+,-256}<%bb4>))<nuw><nsw> umin {%tmp3,+,-256}<%bb4>))<nuw><nsw> umin {%tmp3,+,-256}<%bb4>))<nuw><nsw> umin {%tmp3,+,-256}<%bb4>)) U: [7,264) S: [7,264) Exits: <<Unknown>> LoopDispositions: { %bb4: Computable, %bb53: Invariant }
228228
; CHECK-NEXT: %tmp49 = ashr i32 %tmp48, 3
229-
; CHECK-NEXT: --> %tmp49 U: [-268435456,268435456) S: [-268435456,268435456) Exits: <<Unknown>> LoopDispositions: { %bb4: Variant, %bb53: Invariant }
229+
; CHECK-NEXT: --> %tmp49 U: [0,128) S: [0,128) Exits: <<Unknown>> LoopDispositions: { %bb4: Variant, %bb53: Invariant }
230230
; CHECK-NEXT: %tmp51 = select i1 %tmp50, i32 %tmp49, i32 0
231-
; CHECK-NEXT: --> %tmp49 U: [-268435456,268435456) S: [-268435456,268435456) Exits: <<Unknown>> LoopDispositions: { %bb4: Variant, %bb53: Invariant }
231+
; CHECK-NEXT: --> %tmp49 U: [0,128) S: [0,128) Exits: <<Unknown>> LoopDispositions: { %bb4: Variant, %bb53: Invariant }
232232
; CHECK-NEXT: %tmp52 = zext i32 %tmp51 to i64
233-
; CHECK-NEXT: --> (zext i32 %tmp49 to i64) U: [0,4294967296) S: [0,4294967296) Exits: <<Unknown>> LoopDispositions: { %bb4: Variant, %bb53: Invariant }
233+
; CHECK-NEXT: --> (zext i32 %tmp49 to i64) U: [0,128) S: [0,128) Exits: <<Unknown>> LoopDispositions: { %bb4: Variant, %bb53: Invariant }
234234
; CHECK-NEXT: %tmp54 = phi i64 [ undef, %bb4 ], [ %tmp59, %bb53 ]
235235
; CHECK-NEXT: --> {undef,+,1}<nsw><%bb53> U: full-set S: full-set Exits: (-1 + (zext i32 %tmp49 to i64))<nsw> LoopDispositions: { %bb53: Computable, %bb4: Variant }
236236
; CHECK-NEXT: %tmp55 = trunc i64 %tmp54 to i32
237237
; CHECK-NEXT: --> {(trunc i64 undef to i32),+,1}<%bb53> U: full-set S: full-set Exits: (-1 + %tmp49)<nsw> LoopDispositions: { %bb53: Computable, %bb4: Variant }
238238
; CHECK-NEXT: %tmp56 = shl nsw i32 %tmp55, 3
239-
; CHECK-NEXT: --> {(8 * (trunc i64 undef to i32)),+,8}<%bb53> U: [0,-7) S: [-2147483648,2147483641) Exits: (-8 + (8 * %tmp49)<nsw>) LoopDispositions: { %bb53: Computable, %bb4: Variant }
239+
; CHECK-NEXT: --> {(8 * (trunc i64 undef to i32)),+,8}<%bb53> U: [0,-7) S: [-2147483648,2147483641) Exits: (-8 + (8 * %tmp49)<nuw><nsw>)<nsw> LoopDispositions: { %bb53: Computable, %bb4: Variant }
240240
; CHECK-NEXT: %tmp57 = sext i32 %tmp56 to i64
241-
; CHECK-NEXT: --> (sext i32 {(8 * (trunc i64 undef to i32)),+,8}<%bb53> to i64) U: [0,-7) S: [-2147483648,2147483641) Exits: (sext i32 (-8 + (8 * %tmp49)<nsw>) to i64) LoopDispositions: { %bb53: Computable, %bb4: Variant }
241+
; CHECK-NEXT: --> (sext i32 {(8 * (trunc i64 undef to i32)),+,8}<%bb53> to i64) U: [0,-7) S: [-2147483648,2147483641) Exits: (-8 + (8 * (zext i32 %tmp49 to i64))<nuw><nsw>)<nsw> LoopDispositions: { %bb53: Computable, %bb4: Variant }
242242
; CHECK-NEXT: %tmp58 = getelementptr inbounds i8, ptr null, i64 %tmp57
243-
; CHECK-NEXT: --> ((sext i32 {(8 * (trunc i64 undef to i32)),+,8}<%bb53> to i64) + null) U: [0,-7) S: [-2147483648,2147483641) Exits: ((sext i32 (-8 + (8 * %tmp49)<nsw>) to i64) + null) LoopDispositions: { %bb53: Computable, %bb4: Variant }
243+
; CHECK-NEXT: --> ((sext i32 {(8 * (trunc i64 undef to i32)),+,8}<%bb53> to i64) + null) U: [0,-7) S: [-2147483648,2147483641) Exits: (-8 + (8 * (zext i32 %tmp49 to i64))<nuw><nsw> + null) LoopDispositions: { %bb53: Computable, %bb4: Variant }
244244
; CHECK-NEXT: %tmp59 = add nsw i64 %tmp54, 1
245245
; CHECK-NEXT: --> {(1 + undef),+,1}<nsw><%bb53> U: full-set S: full-set Exits: (zext i32 %tmp49 to i64) LoopDispositions: { %bb53: Computable, %bb4: Variant }
246246
; CHECK-NEXT: %tmp62 = add nuw nsw i64 %tmp5, 1

‎llvm/test/Analysis/ValueTracking/knownbits-select-from-cond.ll

Lines changed: 4 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -6,7 +6,7 @@ define i8 @select_condition_implies_highbits_op1(i8 %xx, i8 %y) {
66
; CHECK-NEXT: [[X:%.*]] = and i8 [[XX:%.*]], 15
77
; CHECK-NEXT: [[COND:%.*]] = icmp ult i8 [[Y:%.*]], 3
88
; CHECK-NEXT: [[SEL:%.*]] = select i1 [[COND]], i8 [[Y]], i8 [[X]]
9-
; CHECK-NEXT: [[R:%.*]] = add i8 [[SEL]], 32
9+
; CHECK-NEXT: [[R:%.*]] = or disjoint i8 [[SEL]], 32
1010
; CHECK-NEXT: ret i8 [[R]]
1111
;
1212
%x = and i8 %xx, 15
@@ -21,7 +21,7 @@ define i8 @select_condition_implies_highbits_op2(i8 %xx, i8 %y) {
2121
; CHECK-NEXT: [[X:%.*]] = and i8 [[XX:%.*]], 15
2222
; CHECK-NEXT: [[COND:%.*]] = icmp ugt i8 [[Y:%.*]], 3
2323
; CHECK-NEXT: [[SEL:%.*]] = select i1 [[COND]], i8 [[X]], i8 [[Y]]
24-
; CHECK-NEXT: [[R:%.*]] = add i8 [[SEL]], 32
24+
; CHECK-NEXT: [[R:%.*]] = or disjoint i8 [[SEL]], 32
2525
; CHECK-NEXT: ret i8 [[R]]
2626
;
2727
%x = and i8 %xx, 15
@@ -37,7 +37,7 @@ define i8 @select_condition_implies_highbits_op1_and(i8 %xx, i8 %y, i1 %other_co
3737
; CHECK-NEXT: [[COND0:%.*]] = icmp ult i8 [[Y:%.*]], 3
3838
; CHECK-NEXT: [[COND:%.*]] = and i1 [[COND0]], [[OTHER_COND:%.*]]
3939
; CHECK-NEXT: [[SEL:%.*]] = select i1 [[COND]], i8 [[Y]], i8 [[X]]
40-
; CHECK-NEXT: [[R:%.*]] = add i8 [[SEL]], 32
40+
; CHECK-NEXT: [[R:%.*]] = or disjoint i8 [[SEL]], 32
4141
; CHECK-NEXT: ret i8 [[R]]
4242
;
4343
%x = and i8 %xx, 15
@@ -54,7 +54,7 @@ define i8 @select_condition_implies_highbits_op2_or(i8 %xx, i8 %y, i1 %other_con
5454
; CHECK-NEXT: [[COND0:%.*]] = icmp ugt i8 [[Y:%.*]], 3
5555
; CHECK-NEXT: [[COND:%.*]] = or i1 [[COND0]], [[OTHER_COND:%.*]]
5656
; CHECK-NEXT: [[SEL:%.*]] = select i1 [[COND]], i8 [[X]], i8 [[Y]]
57-
; CHECK-NEXT: [[R:%.*]] = add i8 [[SEL]], 32
57+
; CHECK-NEXT: [[R:%.*]] = or disjoint i8 [[SEL]], 32
5858
; CHECK-NEXT: ret i8 [[R]]
5959
;
6060
%x = and i8 %xx, 15

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